Which of the following joints primarily allows for rotary movements?

Pivot joints primarily allow for rotary movements due to their unique structure. In a pivot joint, one bone rotates around another, enabling rotational motion. A classic example is the joint between the first and second cervical vertebrae (the atlas and axis), which allows for the head to rotate from side to side. This specific design facilitates the circular motion of one bone around another, making pivot joints ideal for activities that require rotation.

In contrast, other types of joints have different movements associated with them. Ball-and-socket joints, while they permit a wide range of movements, including rotation, also allow for flexion, extension, abduction, and adduction. Hinge joints are limited to movements primarily in one plane, typically allowing only flexion and extension. Saddle joints enable a combination of movements, including up-and-down and side-to-side, but do not specialize in rotary motion like pivot joints do. Therefore, the distinctive capability of pivot joints to support rotary movement makes them the correct answer in this context.